If trash bag has a built-in cinch or ties, cut a straight line across top. Cut open sides and bottom so you have two pieces of equal size.

Tape one piece over window, securing it tightly on all four sides.

Use a grease pencil to draw a simple design that resembles curtains and a valance. It does not need to be perfectly symmetrical. Remove tape and cut out shape.

Tape other piece of bag to a flat surface, then tape cut-out shape on top of it. Use grease pencil to draw a similar, slightly larger shape. There should be some areas where shapes overlap and others where they don’t, adding depth to curtain.

Remove tape, crumple up both pieces, then open. Do it again. (This helps disguise creases in trash bag.)

Secure top and sides of larger piece to window frame with double-stick tape. Tape other piece on top of first.